toolchain/58539: AVX-512 support incomplete/broken

[Thomas Klausner <wiz%NetBSD.org@localhost>]

>Number:         58539
>Category:       toolchain
>Synopsis:       AVX-512 support incomplete/broken
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    toolchain-manager
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Fri Aug 02 10:30:00 +0000 2024
>Originator:     Thomas Klausner
>Release:        NetBSD 10.99.11
>Organization:

>Environment:
	
	
Architecture: x86_64
Machine: amd64

# cpuctl identify 0 | grep AVX
cpu0: features1 0x7ed8320b<MOVBE,POPCNT,AES,XSAVE,OSXSAVE,AVX,F16C,RDRAND>
cpu0: features5 0xf1bf97a9<FSGSBASE,BMI1,AVX2,SMEP,BMI2,ERMS,INVPCID,QM,PQE>
cpu0: features5 0xf1bf97a9<AVX512F,AVX512DQ,RDSEED,ADX,SMAP,AVX512_IFMA>
cpu0: features5 0xf1bf97a9<CLFLUSHOPT,CLWB,AVX512CD,SHA,AVX512BW,AVX512VL>
cpu0: features6 0x405fce<AVX512_VBMI,UMIP,PKU,AVX512_VBMI2,CET_SS,GFNI,VAES>
cpu0: features6 0x405fce<VPCLMULQDQ,AVX512_VNNI,AVX512_BITALG,AVX512_VPOPCNTDQ>
cpu0: xsave features 0x2e7<x87,SSE,AVX,Opmask,ZMM_Hi256,Hi16_ZMM,PKRU>
cpu0: enabled xsave 0xe7<x87,SSE,AVX,Opmask,ZMM_Hi256,Hi16_ZMM>
cpu0: SEF-subleaf1-eax 0x20<AVX512_BF16>

>Description:

While debugging a problem with lang/ghc98 that only I could reproduce
but pho@ not (see http://gnats.netbsd.org/58379), we contacted
upstream and they pointed out that they're using AVX-512 support, and
that that had lead to weird similar problems in the past (on OpenBSD,
it causes SIGILLs; on FreeBSD other unspecified issues).

Their proposed workaround of disabling AVX-512 support fixed the
problem for me, so there must be some problem in the NetBSD AVX-512
support.

>How-To-Repeat:

Build lang/ghc98 (currently 9.8.2) on a system support AVX-512, with
the following line removed from lang/ghc98/Makefile:

CFLAGS+=        -D__STDC_NO_ATOMICS__
>Fix:
Yes, please.

OpenBSD fixed their AVX-512 support with, I think:

https://codeberg.org/openbsd/src/commit/c0f33c9875c4ab47e986b698610630b6cbf21c6c

>Unformatted: